Allergy Flashcards
How can a diagnosis of seasonal allergic rhinitis be made?
based on history and examination alone - further investigations reserved for refractory cases
What are 3 groups allergic rhinitis can be categorised into?
- season allergic rhinitis (hayfever - tree pollen, grass, mould spores, weeds)
- perennial rhinitis - throughout the year (house dust mites, domestic pets)
- occupational rhinitis - allergics at work e.g. flour, wood dust, latex
What information can give a clue to the allergic in seasonal rhinitis?
- symptoms timing - tree pollen = spring
- grass pollen = spring-summer
- weed pollen = spring- autumn
If the causative agent is not clear in allergic rhinitis, what are 3 tests to consider?
- skin prick test
- blood assays - IgE concentrations via RAST or ELISA
- CT - if suspect chronic rhinosinusitis / neoplasia
What are 3 drugs that can suppress the response to skin prick testing?
- antihistamines
- steroids
- tricyclic antidepressants
What are 7 ways to diminish exposure to house dust mites?
- house dust mite impermeable covers for mattresses and pillows
- synthetic pillows
- acrylic duvets
- soft toys off bed
- wash bedding once a week high temp
- wooden or hard floor coverings (not carpets)
- fitted blinds (not curtains)
What are 3 key treatments for allergic rhinitis?
- topical nasal antihistamines e.g. azelastine - first line for PRN treatment
- oral antihistamines e.g. cetirizine, loratadine
- topical intranasal steroids e.g. beclomethasone, mometasone - first line for pregnant / breastfeeding patients
What is the management of non-IgE mediated food allergy?
Eliminate for 2-6 weeks then gradually re-introduce e.g. egg ladder, dietitian guidance
What type of hypersensitivity reaction is contact dermatitis?
type IV reaction
What is the mechanism of type I hypersensitivity reactions?
- anaphylactic
- antigen reacts with IgE bound to mast cells
What are 2 examples of type I hypersensitivity reactions?
- anaphylaxis
- atopy e.g. asthma, eczema and hayfever
What is the mechanism of type II hypersensitivity reactions?
cell bound: IgG or IgM binds to antigen on cell surface
What are 7 examples of type II hypersensitivity reactions?
- autoimmune haemolytic anaemia
- ITP
- Goodpasture’s syndrome
- Pernicious anaemia
- Acute haemolytic transfusion reactions
- Rheumatic fever
- Pemphigus vulgaris bullous pemphigoid
What is the mechanism of type III hypersensitivity rections?
immune complex - free antigen and antibody (IgG, IgA) combine
What are 4 examples of type III hypersensitivity reactions?
- serum sickness
- systemic lupus erythematosus
- post-streptococcal glomerulonephritis
- extrinsic allergic alveolitis (acute phase)
What is the mechanism of type IV hypersensitivity reactions?
T-ell mediated
What are 7 examples of type IV hypersensitivity reactions?
- allergic contact dermatitis
- tuberculosis/ tuberculin skin reaction
- graft versus host disease
- scabies
- extrinsic allergic alveolitis (chronic phase)
- multiple sclerosis
- Guillain-Barre syndrome
What is the mechanism of type V sensitivity reactions?
antibodies that recognise and bind to cell surface receptors; either stimulate them or block ligand binding
What are 2 examples of type V hypersensitivity reactions?
- Myasthenia Gravis
- Graves’ disease
Is IV hydrocortisone indicated in the management of anaphylaxis?
no - previously recommended but evidence base poor, now removed in 2021 update
What is the adrenaline dose in anaphylaxis children < 6 months?
0.1 - 0.15 mg (0.1-0.13ml 1 in 1000)
What is the adrenaline dose for anaphylaxis in children 6 months to 6 years?
0.15 mg (0.15 ml 1 in 1000)
What is the adrenaline dose for anaphylaxis in children age 6 - 12 years?
0.3 mg (0.3 ml 1 in 1000)
What is the adrenaline dose for anaphylaxis in children >12y and adults?
0.5 mg (0.5 ml 1 in 1000)
What is the algorithm for anaphylaxis management?
IM adrenaline injection; repeat after 5 minutes if necessary
if symptoms persist despite 2 doses - IV fluids, IV adrenaline infusion (seek expert help)
What is the dosing for IV adrenaline infusion for refractory anaphylaxis?
1mg (1ml of 1mg/ml 1:1000) adrenaline in 100ml of 0.9% sodium chloride
in adults + children: 0.5-1.0 ml/kg/hour initially, then titrate according to clinical response
What medication should be given following resolution of anaphylaxis?
non-sedating oral antihistamines (in preference to chlorphenamine) - esp if persistngin skin symptoms (urticaria/angioedema)
How long do serum tryptase levels remain elevated after anaphylaxis?
up to 12h
What should happen to all patients with a new diagnosis of anaphylaxis?
refer to specialist allergy clinic; give 2 adrenaline injectors as interim measure before assessment (unless drug-induced)
What are 4 criteria for a fast-track discharge after anaphylaxis (after 2 hours of symptom resolution)?
- good response to single dose adrenaline
- complete resolution of symptoms
- given adrenaline auto-injector + trained how to use it
- adequate supervision following discharge
What are 2 criteria for discharge after 6 hours following anaphylaxis symptom resolution?
- 2 doses IM adrenaline needed
- previous biphasic reaction
What are 5 reasons to discharge minimum 12 hours after anaphylaxis symptom resolution?
- severe reaction requiring >2 doses of IM adrenaline
- patient has severe asthma
- possibility of ongoing reaction e.g. slow release medication
- patient presents late at night
- patient in areas where access to emergency access care may be difficult
What is used as a control for skin prick testing?
histamine (positive) and sterile water (negative) controls
After how long can a skin prick test be interpreted?
15 minutes
What type of allergens is skin prick testing used for?
food allergies + pollen
When is radioallergosorbent testing (RAST) used?
- when skin prick tests not suitable e.g. extensive eczema, patient taking antihistamines
- used for food allergies, inhaled allergens (e.g. pollen) and wasp/bee venom
How does RAST testing work?
- determines amount of IgE that reacts specifically with suspected or known allergens e.g. IgE to egg protein
- results given in grades from 0 (negative) to 6 (strongly positive)
What condition is skin patch testing useful for?
useful for contact dermatitis, allergens + irritants
How many allergens can be tested for with skin patch testing?
30-40 minutes
How long does it take before skin patch testing can be interpreted?
48 hours - removed + read by dermatologist
